Call number: LD2668 .T4 1983 J66 / Master of Science

This thesis presents the results of a study of the mechanisms responsible for limiting the laser pulse duration obtainable in xenon chloride lasers which are excited by UV-preionized, self-sustained gas discharges. The xenon chloride laser system, the principal emission band of which is centred around 308 nm, belongs to the class of high pressure gas lasers known as 'rare-gas halides'(RGH). RGH lasers are now well known for their high peak power output at a number of wavelengths from 193 nm to 353 nm in the ultraviolet region of the spectrum. To date, however, they have only been operated in the pulsed mode with laser pulse durations of ^~1000 ns for devices employing electron beam excitation and ^~30 ns for devices employing transverse discharge excitation. There is no a priori kinetic limitation which prevents RGH lasers from operating in the CW mode, and an attempt to extend the duration of the laser pulse would enable the quality of laser output to be improved. The laser pulse duration of a discharge excited XeCl^* laser was extended by about one order of magnitude - to 270 ns FWHM - by the use of a distributed resistance electrode to stabilize the discharge. The typical gas mixture used in the laser was ~2 atm of Ne (buffer gas), ~25 mbar of Xe, and 2.5 mbar of HC1. However, the laser pulse duration obtained was considerably shorter than the 500 ns duration, 2000 A peak current, discharge excitation pulse. The cause of this difference between the duration of the laser output pulse and the discharge current pulse was found by carrying out a comprehensive parametric study of the laser, combined with a detailed spectroscopic analysis and the results of a semi-empirical computer model. Two interrelated factors were identified as being responsible for the short duration of the laser output: namely, a temporal collapse of the discharge volume and a spatially non-uniform depletion of the HCl within this volume. The experimental results presented here contradict an earlier theory which ascribed the onset of discharge instabilities in RGH lasers to step-wise ionization of the minority rare gas atoms, and which attributed stability enhancement properties to the electronegative halogen gases used in RGH lasers.

The solubility of the noble gases is temperature dependent. Other factors influencing solubility are the system pressure, the solute content of the water, and gravitational potentials. Most of the noble gases dissolved in ground water are from chemical equilibrium with the atmosphere. This equilibrium takes place in the recharge zone of the aquifer, typically in the soil. The final noble-gas concentrations are determined by the temperature, the elevation, the alteration of soil-gas composition by organisms, and soil-temperature gradients (which are in part a result of water-table depth and recharge rates). If the effects of temperature can be separated from the other influences, and if the noble-gas concentrations are not altered after recharge water enters the saturated zone, variations in recharge temperature with time may be determined by measuring the noble gases in dated ground-water samples. However, analysis of available data indicates that noble-gas concentrations frequently change after recharge. This change is usually the result of reequilibration with a biogenicgas phase produced within the aquifer, or from contact with air. In order to extend the calculation of recharge history to samples with complex histories of gas equilibrium a general equation for two stage equilibrium was derived. The variables in this equation are the initial temperature and pressure of equilibrium, the final temperature and pressure of equilibrium, and the molar water-to-gas ratio at the second equilibration. An equation of this type is constructed for each of the gases: neon, argon, krypton and xenon. These equations are solved simultaneously for four of the variables listed above while the value of one is assumed. Graphical techniques for determining which assumptions to use are presented. Ground-water samples were collected in glass tubes and analyzed by gas chromatograph-mass spectrometer, using double isotope dilution standardization. The analytical method is still developmental. Field sampling was undertaken in two locations, the Milk River aquifer of southern Alberta, Canada, and the Carrizo sand aquifer in southern Texas, in order to test the method. The preliminary data obtained may show correlation with known Holocene-Pleistocene climatic fluctuations, encouraging further development of the analytical technique and field research. Finally, a method for interpreting the climatic implications of oxygen and hydrogen isotope information from ground water in conjunction with noble-gas data is given.

Thesis (Ph. D.)--University of Missouri-Columbia, 2001. / Typescript. Vita. Includes bibliographical references (leaves 80-86). Also available on the Internet.

Thesis (Ph. D.)--University of Missouri-Columbia, 2001. / Typescript. Vita. Includes bibliographical references (leaves 80-86). Also available on the Internet.

Thesis (Ph. D.)--University of Chicago, Dept of Chemistry, August 2003. / Includes bibliographical references. Also available on the Internet.

No description available.

Bibliography: leaves 111-116 / xi, 170 leaves : ill ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.)--University of Adelaide, 1984

No description available.

Thesis (Ph. D.)--Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 2007. / "September 2007". "Joint Program in Oceanography/Applied Ocean Science and Engineering"--Cover. Title from Web page (viewed on Mar. 24, 2008). Includes bibliographical references (p. 215-225).